MULTILAYER INTERLAYERS HAVING HIGH Tg AND HIGH MODULUS

ABSTRACT

A multilayer interlayer structure having a low Mw/high Tg layer and a high Mw layer, the interlayer having a high E′ modulus and a higher Tg. The high Tg layer has a Tg of at least 50° C. and a weight average molecular weight of not more than 160,000. The high Mw layer has a molecular weight greater than 160,000. The interlayer structure has increased stiffness without having to increase its thickness, and has an increased Tg to enable the structure to be used in applications that require good modulus at outdoor temperatures.

1. CROSS REFERENCE TO RELATED APPLICATION(S)

This Application is a continuation of U.S. patent application Ser. No.14/954,606 filed on Nov. 30, 2015, now pending, which claims the benefitof U.S. Provisional Patent Application Ser. No. 62/088,837, filed Dec.8, 2014, now expired, the entire disclosure of which is incorporated byreference herein.

2. FIELD OF THE INVENTION

The present invention relates to multilayer poly(vinyl acetal)interlayers, and more particularly to multilayer poly(vinyl acetal)interlayers having a high glass transition temperature and that are morerigid at higher temperatures. The multilayer poly(vinyl acetal)interlayers having a higher glass transition temperature and higherrigidity can be used as an interlayer for laminated glass in moredemanding structural applications that experience higher ambienttemperature conditions.

3. BACKGROUND OF THE INVENTION

Generally, laminated multiple layer glass panels refer to a laminatecomprised of a polymer sheet or interlayer sandwiched between two panesof glass. The laminated multiple layer glass panels are commonlyutilized in architectural window applications, in the windows of motorvehicles, airplanes, trains and other modes of transporting people andgoods, and in photovoltaic solar panels. The first two applications arecommonly referred to as laminated safety glass. The main function of theinterlayer in the laminated safety glass is to absorb energy resultingfrom impact or force applied to the glass, keep the layers of glassbonded even when the force is applied and the glass is broken, andprevent the glass from breaking up into sharp pieces. Additionally, theinterlayer generally gives the glass a much higher sound insulationrating, reduces UV and/or IR light transmission, and enhances theaesthetic appeal of the associated window. In regards to thephotovoltaic applications, the main function of the interlayer is toencapsulate the photovoltaic solar panels which are used to generate andsupply electricity in commercial and residential applications.

The interlayer is generally produced by mixing a polymer resin such aspoly(vinyl acetal) with one or more plasticizers and melt blending ormelt processing the mix into a sheet by any applicable process or methodknown to one of skill in the art, including, but not limited to,extrusion. Other additional additives may optionally be added forvarious other purposes. After the interlayer sheet is formed, it istypically collected and rolled for transportation and storage and forlater use in the multiple layer glass panels, as described below.Interlayer sheets of the appropriate size and thickness are sometimescut, stacked and shipped in such stacks for later use in the multiplelayer glass panels.

The following offers a simplified description of the manner in whichmultiple layer glass panels are generally produced in combination withthe interlayers. First, at least one interlayer sheet, either monolithicor comprising several coextruded or prelaminated layers (“multilayerinterlayers”), is placed between two substrates, such as glass panels,and any excess interlayer is trimmed from the edges, creating anassembly. It is not uncommon for multiple monolithic interlayer sheetsto be placed within the two substrates creating a multiple layer glasspanel with multiple monolithic interlayers. It is also not uncommon formultilayer interlayer sheets that comprise several coextruded orprelaminated layers, or multilayer interlayer sheets in combination withmonolithic interlayer sheets to be placed within the two substratescreating a multiple layer glass panel with multilayer interlayers. Then,air is removed from the assembly by an applicable process or methodknown to one of skill in the art; e.g., through nip rollers, vacuum bag,vacuum ring, vacuum laminator, or another de-airing mechanism.Additionally, the interlayer is partially press-bonded to the substratesby any method known to one of ordinary skill in the art. In a last step,in order to form a final unitary structure, this preliminary bonding isrendered more permanent by a high temperature and pressure laminationprocess known to one of ordinary skill in the art such as, but notlimited to, autoclaving.

A structural poly(vinyl acetal) interlayer, Saflex™ DG41 (a poly(vinylbutyral) polymer (“DG41”) having a weight average molecular weight(M_(w)) of about 170,000), is commercially available for applications inthe architectural space. While the glass transition temperature (“Tg”)of DG41 is suitable for many architectural applications (˜46° C.), itwould be desirable to raise the Tg of the interlayer to take advantageof a full range of applications it could have in the architecturalspace. Higher Tg products are desirable as they may be suitable for moredemanding architectural applications that are exposed to consistentlyhigher temperatures, especially those that require high modulus athigher ambient temperatures.

One methodology to increase the Tg of the poly(vinyl acetal) interlayeris to reduce the amount of plasticizer in the poly(vinyl acetal) resin.Reducing the amount of plasticizer, however, decreases the flowabilityof the polymer composition making processing quite difficult. DG41 isalready difficult to process in extrusion compared to other more highlyplasticized polymers owing to its lower level of plasticizer level ofabout 20 parts of plasticizer per hundred parts resin. The lowplasticizer level in DG41 decreases its flowability, resulting inreduction in melt flowability and manifests itself as a large pressuredrop between the head of the extruder or the melt pump to the back faceof the die plate with a corresponding drop in extruder output orcapacity. Although the processing of DG41 is difficult, it remains at anacceptable level. However, attempting to increase the Tg of thepoly(vinyl acetal) interlayer by further dropping the amount ofplasticizer may so decrease the flowability of the polymer compositionso as to make its processing unacceptable.

Increasing the plasticizer level assists in improving the polymerflowability, thereby facilitating processing in the extruder manifestingitself as a lower pressure between the extruder head or melt pump to theback face of the die. However, increasing the plasticizer level alsodecreases the Tg of the interlayer.

It would be desirable to provide a poly(vinyl acetal) thermoplasticresin that has both an enhanced Tg and high E′ modulus (which is ameasure of the layer's stiffness or rigidity), and that has goodflowability. The increase in Tg cannot be accomplished by a mere drop inthe amount of plasticizer since, as already mentioned, the processingconditions suffer through large pressure drops resulting in a loss inoutput capacity. It would also be desirable to provide the flexibilityof not having to increase the thickness of the layers in order toachieve a higher interlayer rigidity.

4. SUMMARY OF THE INVENTION

The inventors have discovered a multilayer interlayer that has elevatedTg and higher E′ modulus, with the flexibility if desired of maintainingthe same thickness of the multilayer interlayer. The composition has ahigh melt flow index, thereby providing a composition that is moreflowable.

There is now provided a multilayer interlayer structure comprising:

(A) a high M_(w) layer comprising a poly(vinyl acetal) resin having aweight average molecular weight (M_(w)) greater than 160,000; and

(B) a high Tg layer comprising a poly(vinyl acetal) resin having aweight average molecular weight (M_(w)) of 160,000 or less and a glasstransition temperature (Tg) of at least 46° C. The high glass transitiontemperature (Tg) layer desirably has a melt flow index of at least 0.65grams/10 minutes when measured at 190° C. and under a load of 2.16kilograms

Also provided is a multilayer interlayer comprising:

(A) a high M_(w) layer comprising a poly(vinyl acetal) resin having aweight average molecular weight (M_(w)) greater than 160,000 and aplasticizer, wherein the high M_(w) layer has a glass transitiontemperature (Tg) of less than 46° C.; and

(B) a high Tg layer comprising a poly(vinyl acetal) resin having aweight average molecular weight (M_(w)) of 160,000 or less and aplasticizer in an amount of from 2 to 20 parts per hundred parts of thepoly(vinyl acetal) resin, wherein the high Tg layer has a glasstransition temperature (Tg) of at least 46° C.

Also provided is a multilayer interlayer comprising:

(A) a high M_(w) layer comprising a poly(vinyl acetal) resin having aweight average molecular weight (M_(w)) greater than 160,000 and aplasticizer, wherein the high M_(w) layer has a glass transitiontemperature (Tg) of less than 46° C.;

(B) a high Tg layer comprising a poly(vinyl acetal) resin having aweight average molecular weight (M_(w)) of 160,000 or less and aplasticizer in an amount of from 2 to 20 parts per hundred parts of thepoly(vinyl acetal) resin, wherein the high Tg layer has a glasstransition temperature (Tg) of at least 46° C.; and

(C) a high M_(w) layer comprising a poly(vinyl acetal) resin having aweight average molecular weight (M_(w)) greater than 160,000 and aplasticizer, wherein the high M_(w) layer has a glass transitiontemperature (Tg) of less than 46° C.,

wherein the high Tg layer is disposed between the high M_(w) layers.

5. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a glass panel containing a multilayerinterlayer.

FIG. 2 is an illustration of an extrusion device for extrudingcompositions useful to make interlayer sheets.

FIG. 3 is a graph showing the rigidity of the interlayers as determinedby modulus for a variety of poly(vinyl acetal) resins having differentglass transition temperature (Tg) values, some of which are high glasstransition temperature (Tg) core layers.

6. DETAILED DESCRIPTION OF THE INVENTION

The term “multilayer interlayer” is at least two layers of poly(vinylacetal) resin. The multiple layers may be separately extruded layers,co-extruded layers, or any combination of separately and co-extrudedlayers. Thus the multilayered interlayer could comprise, for example:two or more single-layer interlayers combined together (“plural-layerinterlayer”); two or more layers co-extruded together (“co-extrudedinterlayer”); two or more co-extruded interlayers combined together; acombination of at least one single-layer interlayer and at least oneco-extruded interlayer; and a combination of at least one plural-layerinterlayer and at least one co-extruded interlayer.

A multilayered interlayer comprises at least two polymer layers (e.g., asingle layer or multiple layers co-extruded) disposed in direct orindirect contact with each other, desirably in direct contact with eachother, wherein each layer comprises a polymer resin, as detailed morefully below. When three or more layers are employed, at least three ofthe layers can be referred to as skin layers and one or more one or morecore layers. As used herein, “skin layer” generally refers to outerlayers of the interlayer and “one or more core layers” generally refersto one or more of the inner layer(s) disposed between the skin layers.At least one side of a one or more core layers can be in direct contactwith at least one side of a skin layers or may be indirect contact witha skin layers, such as through a polymer layer. Thus, one exemplarymultilayer embodiment would be: high M_(w)/high Tg/high M_(w) (e.g. askin layer/core layer/skin layer), or a high M_(w)/high Tg (e.g.skin/core), high M_(w)/high Tg/high M_(w)/polymer film (e.g.skin/core/skin/polymer), or high M_(w)/high Tg/high Tg/high M_(w) (e.g.skin/core/core/skin), or high M_(w)/high Tg/high Tg/high M_(w)/polymer(e.g. skin/core/core/skin/polymer), or a high M_(w)/high Tg/highM_(w)/high Tg/high M_(w). The multilayer interlayer can also have morethan three layers (e.g., 4, 5, 6, or up to 10 or more individual layers,so long as at least one of the layers is a high M_(w) layer and one is ahigh Tg layer). The multilayer interlayer can contain two, three, four,or more of the high M_(w) layers, and two or more of them can be indirect contact with each other or with a high Tg layer or with othertypes of layers. The multilayer interlayer can contain two, three, four,or more high Tg layers, and two of more of them can be in direct contactwith each other or with the high M_(w) layer or with other types oflayers. Desirably, in the multilayer interlayer structure having atleast three layers, at least one of the high Tg layers is disposedbetween two high M_(w) layers, or put another way, forms one or morecore layers. By disposed is meant its location and the layer does notnecessarily have to be in direct contact with the reference layers.Desirably, in a multilayer interlayer structure having at least 3layers, the multilayer has at least 2 outer layers having a high M_(w)resin, or put another way, forms one or more skin layers.

There is now provided a multilayer interlayer structure comprising:

(A) a high M_(w) layer comprising a poly(vinyl acetal) resin having aweight average molecular weight (M_(w)) greater than 160,000; and

(B) a high Tg layer comprising a poly(vinyl acetal) resin having aweight average molecular weight (M_(w)) of 160,000 or less and a glasstransition temperature (Tg) of at least 46° C.

The poly(vinyl acetal) resin in both the high M_(w) and high Tg layersis a thermoplastic resin, but the poly(vinyl acetal) resin in the highM_(w) layer and high Tg layer may be different types of poly(vinylacetal) resin or have different properties, as further described below.Their method of manufacture is not limited. The poly(vinyl acetal) resincan be produced by known aqueous or solvent acetalization processes,such as by reacting PVOH with an aldehyde such as butyraldehyde in thepresence of an acid catalyst, separation, stabilization, and drying ofthe resin. Such acetalization processes are disclosed, for example, inU.S. Pat. Nos. 2,282,057 and 2,282,026 and Vinyl Acetal Polymers, inEncyclopedia of Polymer Science & Technology, 3rd edition, Volume 8,pages 381-399 (2003), the entire disclosures of which are incorporatedherein by reference.

Poly(vinyl acetal) resins typically have a residual hydroxyl content, anester content, and an acetal content. As used herein, residual hydroxylcontent (calculated as PVOH) refers to the weight percent of moietieshaving a hydroxyl group remaining on the polymer chains. For example,poly(vinyl acetal) can be manufactured by hydrolyzing poly(vinylacetate) to PVOH, and then reacting the PVOH with an aldehyde, such asbutyraldehyde, propionaldehyde, and the like, and desirablybutyraldehyde, to make a polymer having repeating vinyl butyral units.In the process of hydrolyzing the poly(vinyl acetate), typically not allof the acetate side groups are converted to hydroxyl groups. Further,reaction with butyraldehyde typically will not result in the conversionof all hydroxyl groups on the PVOH to acetal groups. Consequently, inany finished poly(vinyl butyral), there typically will be residual estergroups such as acetate groups (as vinyl acetate groups) and residualhydroxyl groups (as vinyl hydroxyl groups) as side groups on the polymerchain and acetal (e.g. butyral) groups (as vinyl acetal groups). As usedherein, residual hydroxyl content is measured on a weight percent basisper ASTM 1396.

An example of a polyvinyl butyral structure is used to furtherillustrate how the weight percentages are based from the moiety unit towhich is bonded the relevant pendant group:

Taking the above structure of a polyvinyl butyral, the butyral or acetalcontent is based on the weight percentage of the unit A in the polymer,and OH content is based on the weight percentage of the unit B in thepolymer (a polyvinyl OH moiety or PVOH), and the acetate or estercontent is based on the weight percentage of unit C in the polymer.

Notably, for a given type of plasticizer, the compatibility of theplasticizer in the polymer is largely determined by the hydroxyl contentof the polymer. Polymers with greater residual hydroxyl content aretypically correlated with reduced plasticizer compatibility or capacity,typically due to the hydrophobicity of the plasticizer being morecompatible with fewer hydrophilic groups present on the polymer chain.Conversely, polymers with a lower residual hydroxyl content typicallywill result in increased plasticizer compatibility or capacity.Generally, this correlation between the residual hydroxyl content of apolymer and plasticizer compatibility/capacity can be manipulated andexploited to allow for addition of the proper amount of plasticizer tothe polymer resin and to stably maintain differences in plasticizercontent between multiple interlayers.

The hydroxyl group content of the poly(vinyl acetal) resin used to makethe composition or a layer is not particularly limited, but suitableamounts are from at least about 6, or at least about 8, or at leastabout 10, or at least about 11, or at least about 12, or at least about13, or at least about 14, or at least about 15, or at least about 16, orat least about 17, and in each case up to about 35 wt. % PVOH. Forexample, suitable weight percent (wt. %) hydroxyl groups rangescalculated as PVOH include about 6 to 35, or 6 to 30, or 6 to 25, or 6to 23, or 6 to 20, or 6 to 18, or 6 to 17, or 6 to 16, or 6 to 15, or 7to 35, or 7 to 30, or 7 to 25, or 7 to 23, or 7 to 20, or 7 to 18, or 7to 17, or 7 to 16, or 7 to 15, or 8 to 35, or 8 to 30, or 8 to 25, or 8to 23, or 8 to 20, or 8 to 18, or 8 to 17, or 8 to 16, or 8 to 15, or 9to 35, or 9 to 30, or 9 to 25, or 9 to 23, or 9 to 20, or 9 to 18, or 9to 17, or 9 to 16, or 9 to 15, or 10 to 35, or 10 to 30, or 10 to 25, or10 to 23, or 10 to 20, or 10 to 18, or 10 to 17, or 10 to 16, or 10 to15, or 11 to 35, or 11 to 30, or 11 to 25, or 11 to 23, or 11 to 20, or11 to 18, or 11 to 17, or 11 to 16, or 11 to 15, or 12 to 35, or 12 to30, or 12 to 25, or 12 to 23, or 12 to 20, or 12 to 18, or 12 to 17, or12 to 16, or 12 to 15, or 13 to 35, or 13 to 30, or 13 to 25, or 13 to23, or 13 to 20, or 13 to 18, or 13 to 17, or 13 to 16, or 13 to 15, or14 to 35, or 14 to 30, or 14 to 25, or 14 to 23, or 14 to 20, or 14 to18, or 14 to 17, or 14 to 16, or 14 to 15, or 15 to 35, or 15 to 30, or15 to 25, or 15 to 23, or 15 to 20, or 15 to 18, or 15 to 17, or 15 to16, or 16 to 35, or 16 to 30, or 16 to 25, or 16 to 23, or 16 to 20, or16 to 18, or 16 to 17, or 17 to 35, or 17 to 30, or 17 to 25, or 17 to23, or 17 to 20, or 17 to 18. If desired, the hydroxyl number chosen canbe on the lower end of the ranges. In general, a poly(vinyl acetal)polymer having a lower hydroxyl number has the capability of absorbingmore plasticizer and absorbing it more efficiently.

The poly(vinyl acetal) resin used to make the composition or sheet canalso comprise 20 wt. % or less, or 17 wt. % or less, or 15 wt. % or lessof residual ester groups, including 13 wt. % or less, or 11 wt. % orless, or 9 wt. % or less, or 7 wt. % or less, or 5 wt. % or less, or 4wt. % or less residual ester groups calculated as polyvinyl ester, e.g.,acetate, with the balance being an acetal, preferably butyraldehydeacetal, but optionally including other acetal groups in a minor amount,for example, a 2-ethyl hexanal group (see, for example, U.S. Pat. No.5,137,954, the entire disclosure of which is incorporated herein byreference). Suitable ranges of residual ester groups by wt. % include 0to 20, or 0 to 17, or 0 to 15, or 0 to 13, or 0 to 11, or 0 to 9, or 0to 7, or 0 to 5, or 0 to 4, or 0 to 20, or 0 to 17, or 0 to 15, or 0 to13, or 0 to 11, or 0 to 9, or 0 to 7, or 0 to 5, or 0 to 4, or 1 to 20,or 1 to 17, or 1 to 15, or 1 to 13, or 1 to 11, or 1 to 9, or 1 to 7, or1 to 5, or 1 to 4, or 1 to 20, or 1 to 17, or 1 to 15, or 1 to 13, or 1to 11, or 1 to 9, or 1 to 7, or 1 to 5, or 1 to 4, or 2 to 20, or 2 to17, or 2 to 15, or 2 to 13, or 2 to 11, or 2 to 9, or 2 to 7, or 2 to 5,or 2 to 4, or 3 to 20, or 3 to 17, or 3 to 15, or 3 to 13, or 3 to 11,or 3 to 9, or 3 to 7, or 3 to 5, or 3 to 4, or 3 to 20, or 3 to 17, or 3to 15, or 3 to 13, or 3 to 11, or 3 to 9, or 3 to 7, or 3 to 5, or 3 to4, or 4 to 20, or 4 to 17, or 4 to 15, or 4 to 13, or 4 to 11, or 4 to9, or 4 to 7, or 4 to 5, or 6 to 20, or 6 to 17, or 6 to 15, or 6 to 13,or 6 to 11, or 6 to 9. As with the residual hydroxyl group measurement,the weight percent of residual ester groups (e.g. acetate) is based onthe moiety in the polymer backbone onto which is linked the acetategroup, including the pendant acetate group.

The poly(vinyl acetal) resin used in the invention can also have anacetal content of at least 50 wt. % or at least 55 wt. %, or at least 60wt. %, or at least 65 wt. %, or at least 70 wt. %, or at least 75 wt. %,or at least 80 wt. %, or at least 85 wt. %, or at least 90 wt. %, and ineach case up to 94 wt. %. Suitable ranges include 50 to 94, or 50 to 93,or 50 to 92, or 50 to 91, or 50 to 90, or 50 to 89, or 50 to 88, or 50to 86, or 50 to 85, or 55 to 94, or 55 to 93, or 55 to 92, or 55 to 91,or 55 to 90, or 55 to 89, or 55 to 88, or 55 to 86, or 55 to 85, or 60to 94, or 60 to 93, or 60 to 92, or 60 to 91, or 60 to 90, or 60 to 89,or 60 to 88, or 60 to 86, or 60 to 85, or 65 to 94, or 65 to 93, or 65to 92, or 65 to 91, or 65 to 90, or 65 to 89, or 65 to 88, or 65 to 86,or 65 to 85, or 70 to 94, or 70 to 93, or 70 to 92, or 70 to 91, or 70to 90, or 70 to 89, or 70 to 88, or 70 to 86, or 70 to 85, or 75 to 94,or 75 to 93, or 75 to 92, or 75 to 91, or 75 to 90, or 75 to 89, or 75to 88, or 75 to 86, or 75 to 85, 80 to 94, or 80 to 93, or 80 to 92, or80 to 91, or 80 to 90, or 89 to 89, or 80 to 88, or 80 to 86, or 80 to85, 85 to 94, or 85 to 93, or 85 to 92, or 85 to 91, or 85 to 90, or 85to 89, or 85 to 88, or 85 to 86, or 90 to 94, or 90 to 93, or 90 to 92.

The combination of OH, ester, and acetal ranges is not particularlylimited. Some of the range combinations can be those corresponding tothe checked boxes in Table 1 below.

TABLE 1 OH Ester wt % wt. % 0-20 1-20 2-17 2-15 2-13 2-8 2-6 3-20 3-153-11 3-9 4-20 4-17 4-15 6-25 X X X X X X X X X X X X X 7-25 X X X X X XX X X 8-25 X X X X X X 9-25 X X X 10-25  X X X 6-23 X X X X X X X X X XX X X 8-23 X X x X X 9-23 X X 6-20 X X X X X X X X X X X X X 8-20 X X xX X 9-20 X X 10-20  X X 6-18 X X X X X X X X X X X X X 9-18 X X 10-18  XX 6-15 X X X X X X X X X X X X X 8-15 X X X X X 10-15  X X Acetal Wt. %50-94 65-89 70-92 70-88 90-92 70-91 75-91 65-91 70-91 75-91 65-89 75-8970-88 75-88

The acetal groups can be vinyl propynal groups, vinyl butyral groups,and the like, and are desirably vinyl butyral groups.

The high M_(w) layer, or at least one of the skin layers, has a weightaverage molecular weight (M_(w)) of greater than 160,000, preferably atleast 165,000, or at least 170,000, or at least 175,000, or at least180,000, or at least 185,000, and in each case can be up to about250,000 Daltons, as measured by size exclusion chromatography using thelow angle laser light scaftering (SEC/LALLS) method of Cotts and Ouanoin tetra-hydrofuran. The term “molecular weight” means the weightaverage molecular weight (M_(w)). The method for determining themolecular weight as set forth in this description includes usinghexafluorisopropanol as the mobile phase (0.8 mL/minute). Each sample isprepared by weighing approximately 20 milligrams of resin into a 25 mLflask and adding 10 mL of the mobile phase. The flask is then placed inan automated shaking device until the polymer is fully dissolved. Theanalysis is performed using a three-detector system that includes aViscotek GPCmax (with an autosampler, pump, and degasser), a Viscotektriple detector TDA302 (RALL/LALLS, Viscometer, and DRI combination)with a column oven (commercially available from Malvern Instruments,Malvern, UK). The separation is performed by three Viscotek mixed bedcolumns, including a type I-MB (one low and two high range molecularweight) maintained at 45° C. The complete detector set up is calibratedusing a narrow poly(methyl methacrylate) standard (commerciallyavailable from Viscotek) with a reported molecular weight of 93.458, anintrinsic viscosity of 0.615, and a differential index of refraction(dn/dc) value of 0.1875. The refractive index of the mobile phase is1.2649 and a do/dc value of 0.189 is used for PVB. Viscotek Omnisec4.7.0 software (commercially available from Malvern Instruments) is usedfor data calculations.

The high Tg layer, or the one or more core layers, has an M_(w) of160,000 or less, or 155,000 or less, or 150,000 or less, or 145,000 orless, or 140,000 or less, or 135,000 or less, or 130,000 or less, or125,000 or less, or 120,000 or less, or 115,000 or less, or 110,000 orless, or 105,000 or less, or 100,000 or less, or 95,000 or less, or90,000 or less, or 85,000 or less, or 80,000 or less, and in each case,at least 45,000, or at least 50,000.

The lower molecular weight poly(vinyl acetal) resins that can be used inthe high Tg layer allow one to decrease the amount of plasticizer (whichwill increase the Tg of the poly(vinyl acetal) resin) while maintainingequivalent or lower extrusion pressures. By lowering the amount ofplasticizer used, the E′ (storage) modulus can also be increased. Merelylowering the amount of plasticizer to increase the Tg of a conventionalmolecular weight poly(vinyl acetal) resin renders the resin toodifficult to process. Even though there may not necessarily be acorrelation between the molecular weight and the Tg of the poly(vinylacetal) resin at equivalent plasticizer loadings, it has been discoveredthat lowering the molecular weight of the poly(vinyl acetal) resin andlowering the amount of plasticizer allows one to adequately processthermoplastic resins having high Tg values while also providing for anincreased E′ modulus. Thus, it has been found that it is desirable toemploy a lower molecular weight (M_(w)) poly(vinyl acetal) resin forhigh Tg applications.

Examples of suitable M_(w) ranges for the high Tg layers or one or morecore layers include 45,000 to 160,000, or 45,000 to 155,000, or 45,000to 150,000, or 45,000 to 145,000, or 45,000 to 140,000, or 45,000 to135,000, or 45,000 to 130,000, or 45,000 to 125,000, or 45,000 to120,000, or 45,000 to 115,000, or 45,000 to 110,000, or 45,000 to105,000, or 45,000 to 100,000, or 45,000 to 95,000, or 45,000 to 90,000,50,000 to 160,000, or 50,000 to 155,000, or 50,000 to 150,000, or 50,000to 145,000, or 50,000 to 140,000, or 50,000 to 135,000, or 50,000 to130,000, or 50,000 to 125,000, or 50,000 to 120,000, or 50,000 to115,000, or 50,000 to 110,000, or 50,000 to 105,000, or 50,000 to100,000, or 50,000 to 95,000, or 50,000 to 90,000, or 60,000 to 160,000,or 60,000 to 155,000, or 60,000 to 150,000, or 60,000 to 145,000, or60,000 to 140,000, or 60,000 to 135,000, or 60,000 to 130,000, or 60,000to 125,000, or 60,000 to 120,000, or 60,000 to 115,000, or 60,000 to110,000, or 60,000 to 105,000, or 60,000 to 100,000, or 60,000 to95,000, or 60,000 to 90,000, 70,000 to 160,000, or 70,000 to 155,000, or70,000 to 150,000, or 70,000 to 145,000, or 70,000 to 140,000, or 70,000to 135,000, or 70,000 to 130,000, or 70,000 to 125,000, or 70,000 to120,000, or 70,000 to 115,000, or 70,000 to 110,000, or 70,000 to105,000, or 70,000 to 100,000, or 70,000 to 95,000, or 70,000 to 90,000,80,000 to 160,000, or 80,000 to 155,000, or 80,000 to 150,000, or 80,000to 145,000, or 80,000 to 140,000, or 80,000 to 135,000, or 80,000 to130,000, or 80,000 to 125,000, or 80,000 to 120,000, or 80,000 to115,000, or 80,000 to 110,000, or 80,000 to 105,000, or 80,000 to100,000, or 80,000 to 95,000, or 80,000 to 90,000, 90,000 to 160,000, or90,000 to 155,000, or 90,000 to 150,000, or 90,000 to 145,000, or 90,000to 140,000, or 90,000 to 135,000, or 90,000 to 130,000, or 90,000 to125,000, or 90,000 to 120,000, or 90,000 to 115,000, or 90,000 to110,000, or 90,000 to 105,000, or 90,000 to 100,000, or 100,000 to160,000, or 100,000 to 155,000, or 100,000 to 150,000, or 100,000 to145,000, or 100,000 to 140,000, or 100,000 to 135,000, or 105,000 to160,000, or 105,000 to 155,000, or 105,000 to 150,000, or 105,000 to105,000, or 105,000 to 140,000, or 105,000 to 135,000, or 105,000 to130,000, 110,000 to 160,000, or 110,000 to 155,000, or 110,000 to150,000, or 110,000 to 145,000, or 110,000 to 140,000, or 110,000 to135,000, or 110,000 to 130,000.

The compositions of the high M_(w) layers and high Tg layers arepredominately poly(vinyl acetal) types of resin. In this regard, thecompositions of the high M_(w) layers and high Tg layers, and optionallyany one or more additional layers, contain poly(vinyl acetal) in anamount of at least 60 wt. %, or at least 65 wt. %, or at least 70 wt. %,or at least 75 wt. %, or at least 80 wt. %, or at least 85 wt. %, or atleast 90 wt. % or at least 95 wt. %, and in each case up to 98 wt. %. Ineach case, the poly(vinyl acetal) resin is desirably a polyvinyl butyral(“PVB”) resin.

The compositions of the high M_(w) layers and high Tg layers, andoptionally one or more additional layers, also contain at least oneplasticizer. Plasticizers work by embedding themselves between chains ofpolymers, spacing them apart (increasing the “free volume”) and thussignificantly lowering the glass transition temperature (Tg) of thepolymer resin (typically by 0.5 to 4° C./phr), making the materialsofter and more flowable. In this regard, the amount of plasticizer inthe interlayer can be adjusted to affect the glass transitiontemperature values. The glass transition temperature is the temperaturethat marks the transition from the glassy state of the interlayer to theelastic state. In general, higher amounts of plasticizer loading willresult in lower Tg. Conventional, previously utilized multilayerinterlayers generally have a Tg in the range of about 0° C. for acoustic(noise reducing) interlayer up to 46° C. for hurricane, structural andaircraft interlayer applications, which at the upper end of the Tg rangeare difficult to process. An interlayer's glass transition temperatureis also correlated with the stiffness of the interlayer: the higher theglass transition temperature, the stiffer the interlayer. Generally, aninterlayer with a glass transition temperature of 30° C. or higherincreases laminated glass strength and torsional rigidity. A softerinterlayer (generally characterized by an interlayer with a glasstransition temperature of lower than 30° C.), on the other hand,contributes to the sound dampening effect (i.e., the acousticcharacteristics).

The high Tg layer, or one or more core layers, advantageously have a Tgof at least 46° C., or at least 46.5° C., or at least 47° C., or atleast 50.0° C., or at least 51° C., or at least 52° C., or at least 53°C., or at least 54° C., or at least 55° C., or at least 56° C., or atleast 57° C., or at least 58° C., or at least 59° C., or at least 60° C.The upper limit is not particularly limited. It can be up to 80° C., orup to 75° C., or up to 70° C., or up to 65° C. Suitable ranges include46° C.-80° C., or 46° C.-78° C., or 46° C.-75° C., or 46° C.-73° C., or46° C.-70° C., or 46° C.-68° C., or 46° C.-65° C., or 46° C.-63° C., or46.5° C.-80° C., or 46.5° C.-78° C., or 46.5° C.-75° C., or 46.5° C.-73°C., or 46.5° C.-70° C., or 46.5° C.-68° C., or 46.5° C.-65° C., or 46.5°C.-63° C., or 47° C.-80° C., or 47° C.-78° C., or 47° C.-75° C., or 47°C.-73° C., or 47° C.-70° C., or 47° C.-68° C., or 47° C.-65° C., or 47°C.-63° C., or 50° C.-80° C., or 50° C.-78° C., or 50° C.-75° C., or 50°C.-73° C., or 50° C.-70° C., or 50° C.-68° C., or 50° C.-65° C., or 50°C.-63° C., 51° C.-80° C., or 51° C.-78° C., or 51° C.-75° C., or 51°C.-73° C., or 51° C.-70° C., or 51° C.-68° C., or 51° C.-65° C., or 51°C.-63° C., 53° C.-80° C., or 53° C.-78° C., or 53° C.-75° C., or 53°C.-73° C., or 53° C.-70° C., or 53° C.-68° C., or 53° C.-65° C., or 53°C.-63° C., 55° C.-80° C., or 55° C.-78° C., or 55° C.-75° C., or 55°C.-73° C., or 55° C.-70° C., or 55° C.-68° C., or 55° C.-65° C., or 55°C.-63° C., 57° C.-80° C., or 57° C.-78° C., or 57° C.-75° C., or 57°C.-73° C., or 57° C.-70° C., or 57° C.-68° C., or 57° C.-65° C., or 57°C.-63° C.

The glass transition temperature is determined by rheometric dynamicanalysis using the following procedure. The poly(vinyl acetal) sheet ismolded into a sample disc of 25 millimeters (mm) in diameter. Thepoly(vinyl acetal) sample disc is placed between two 25 mm diameterparallel plate test fixtures of a Rheometrics Dynamic Spectrometer II.The poly(vinyl acetal) sample disc is tested in shear mode at anoscillation frequency of 1 Hertz as the temperature of the poly(vinylacetal) sample is increased from −20 to 70° C. at a rate of 2°C./minute. The position of the maximum value of tan delta (damping)plotted as dependent on temperature is used to determine Tg. Experienceindicates that the method is reproducible to within +/−1° C.

As used herein, the amount of plasticizer, or any other component in theinterlayer, can be measured as parts per hundred parts resin (phr), on aweight per weight basis. For example, if 30 grams of plasticizer isadded to 100 grams of polymer resin, then the plasticizer content of theresulting plasticized polymer would be 30 phr. As used herein, when theplasticizer content of the interlayer is given, the plasticizer contentis determined with reference to the phr of the plasticizer in the meltthat was used to produce the interlayer.

The high M_(w) layer or any one or more of the skin layers can containat least 15, or at least 17, or at least 20, or at least 23, or at least25, or at least 27, or at least 30, or at least 32, or at least 35 phrplasticizer, and up to 80, or up to 70, or up to 60, or up to 50, or upto 45, or up to 40, or up to 35, or up to 30 phr plasticizer. Suitableranges of plasticizer in phr within a high M_(w) layer or any one ormore of the skin layers include 15 to 80, or 15 to 70, or 15 to 60, or15 to 50, or 15 to 45, or 15 to 40, or 15 to 35, or 15 to 30, 20 to 80,or 20 to 70, or 20 to 60, or 20 to 50, or 20 to 45, or 20 to 40, or 20to 35, or 20 to 30, 25 to 80, or 25 to 70, or 25 to 60, or 25 to 50, or25 to 45, or 25 to 40, or 25 to 35, or 25 to 30, 30 to 80, or 30 to 70,or 30 to 60, or 30 to 50, or 30 to 45, or 30 to 40, or 30 to 35, or 35to 30, 35 to 80, or 35 to 70, or 35 to 60, or 35 to 50, or 35 to 45, or35 to 40 phr plasticizer.

The Tg of the high M_(w) layer is not particularly limited. It can be,if desired, lower than the Tg of at least one of the high Tg layers,optionally less than 50° C., or less than 46° C. The optionally lower Tgof the high M_(w) layer or skin layer can contribute to a higherglass/interlayer adhesion, or a better ability to absorb impact energy.Optionally, the Tg of one or more or all of the high M_(w) layers or oneor more or all of the skin layers is not greater than 55° C., or notgreater than 52° C., or not greater than 49° C., or not greater than 48°C., or not greater than 47° C., or not greater than 46° C., or less than46° C., or not greater than 45° C., or not greater than 44° C., or notgreater than 43° C., or not greater than 42° C., or not greater than 41°C., or not greater than 40° C., or not greater than 39° C., or notgreater than 38° C., or not greater than 37° C., or not greater than 36°C., or not greater than 37° C., or not greater than 36° C., or notgreater than 35° C., or not greater than 34° C., or not greater than 33°C., or not greater than 32° C., or not greater than 31° C., or notgreater than 30° C., and in each case at least 25° C.

The Tg of the high M_(w) layer or one or more skin layers can, ifdesired, be at least 1° C., or at least 2° C., or at least 3° C., or atleast 4° C., or at least 5° C., or at least 6° C., or at least 7° C., orat least 8° C., or at least 9° C., or at least 10° C., or at least 11°C., or at least 12° C., or at least 13° C., or at least 14° C., or atleast 15° C., or at least 16° C., or at least 17° C., or at least 18° C.less than the Tg of the high Tg layer or one or more one or more corelayers.

The high Tg layer or any of the one or more core layers can contain atleast 5, or at least 8, or at least 10, or at least 13, or at least 15,or at least 17, or at least 20, and up to 28, or up to 25, or up to 23,or up to 20, or up to 18, or up to 17, or up to 15, or up to 13, or upto 10, or up to 9, or up to 8, or up to 7 parts plasticizer per hundredparts of poly(vinyl acetal) resin. Suitable ranges of plasticizer in phrwithin a layer include 5 to 28, or 5 to 25, or 5 to 23, or 5 to 20, or 5to less than 20, or 5 to 19, or 5 to 18, or 5 to 17, or 5 to 15, or 5 to13, or 5 to 10, or 5 to 9, or 5 to 8, or 5 to 7, 8 to 28, or 8 to 25, or8 to 23, or 8 to 20, or 8 to less than 20, or 8 to 19, or 8 to 18, or 8to 17, or 8 to 15, or 8 to 13, or 8 to 10, or 10 to 28, or 10 to 25, or10 to 23, or 10 to 20, or 10 to less than 20, or 10 to 19, or 10 to 18,or 10 to 17, or 10 to 15, or 10 to 13, or 13 to 28, or 13 to 25, or 13to 23, or 13 to 20, or 13 to less than 20, or 13 to 19, or 13 to 18, or13 to 17, or 13 to 15, or 15 to 28, or 15 to 25, or 15 to 23, or 15 to20, or 15 to less than 20, or 15 to 19, or 15 to 18, or 15 to 17, or 17to 28, or 17 to 25, or 17 to 23, or 17 to 20, or 17 to less than 20, or17 to 19, or 17 to 18, 20 to 28, or 20 to 25, or 20 to 23, or 23 to 28,or 23 to 25.

Desirably, the high Tg layer (or one or more one or more core layers)has less plasticizer than the high M_(w) layer (or one or more of theskin layers). Since a reduction in the amount of plasticizer present inhigh Tg layer or one or more core layers contributes toward an increasein Tg, and a higher amount of plasticizer in the high M_(w) layers orskin layer (relative to the high Tg layers or one or more core layers)assists with increasing adhesion to glass, it is desirable to use lessplasticizer in the high Tg layers or one or more core layers than theamount of plasticizer present in one or more of the high M_(w) layers orskin layers. Desirably, the high Tg layers or one or more core layershas at least 2, or at least 4, or at least 5, or at least 7, or at least9, or at least 10, or at least 11, or at least 12, or at least 15, or atleast 17, or at least 19, or at least 20 phr less plasticizer than ispresent in the high M_(w) layers or one or more skin layers.

The adjustments in the amount of plasticizer in the high Tg layers orone or more core layers are made possible by the use of poly(vinylacetal) polymers having a lower molecular weight (M_(w)), and thereduced amount of plasticizer allows one to make a higher Tg layer orone or more core layers, while the lower molecular weight poly(vinylacetal) resin also allows one to make the high Tg layers or core layersat acceptable rates. The increase in Tg also improves the E′ modulus ofthe high Tg layers or one or more core layers, and therefore alsoimproves the E′ modulus of the whole multilayer interlayer. Theadjustment between the selection of molecular weight and the amount ofplasticizer in the high Tg layers or a one or more core layers allowsone to take advantage of a variety of properties and opens up largeprocessing and application windows. For example, if a particularapplication does not require a high end Tg, the invention allows one toincrease the amount of plasticizer to further improve the flowability ofthe polymer and increase the output (capacity) of the extruder whilemaintaining a compositional Tg of at least 46° C. Alternatively, with anincrease in flowability, the capacity or output of the extruder can bemaintained constant while decreasing the extrusion temperature, therebysaving on energy costs. The extrusion temperature is the temperature ofthe polymer at the entrance to the die head. If none of these objectivesare paramount and maximizing the Tg of the interlayer is desired, asnoted above, the amount of plasticizer can be reduced to a lower end ofthe range, made possible with the use of lower molecular weightpolymers, while maintaining reasonable polymer flowability at extrusiontemperatures not exceeding 240° C., or even not exceeding 235° C., oreven not exceeding 230° C. By maintaining extrusion temperatures notexceeding 240° C., the formation of undesirable degradation by-productsis minimized.

The type of plasticizer used in any of the layers is not particularlylimited. The plasticizer can be a compound having a hydrocarbon segmentof 30 or less, or 25 or less, or 20 or less, or 15 or less, or 12 orless, or 10 or less carbon atoms, and in each case at least 6 carbonatoms. Suitable conventional plasticizers for use in these interlayersinclude esters of a polybasic acid or a polyhydric alcohol, amongothers. Suitable plasticizers include, for example, triethylene glycoldi-(2-ethylhexanoate) (“3GEH”), triethylene glycol di-(2-ethylbutyrate),triethylene glycol diheptanoate, tetraethylene glycol diheptanoate,dihexyl adipate, dioctyl adipate, hexyl cyclohexyladipate, diisononyladipate, heptylnonyl adipate, dibutyl sebacate, butyl ricinoleate,castor oil, dibutoxy ethyl phthalate, diethyl phthalate, dibutylphthalate, trioctyl phosphate, triethyl glycol ester of coconut oilfatty acids, phenyl ethers of polyethylene oxide rosin derivatives, oilmodified sebacic alkyd resins, tricresyl phosphate, and mixturesthereof. A desirable plasticizer is 3GEH.

High refractive index plasticizers may be used in the composition of theinvention, either alone or in combination with another plasticizer.Examples of the high refractive index plasticizers include, but are notlimited to, esters of a polybasic acid or a polyhydric alcohol,polyadipates, epoxides, phthalates, terephthalates, benzoates, toluates,mellitates and other specialty plasticizers, among others. Examples ofhigh refractive index plasticizers include, but are not limited to,dipropylene glycol dibenzoate, tripropylene glycol dibenzoate,polypropylene glycol dibenzoate, isodecyl benzoate, 2-ethylhexylbenzoate, diethylene glycol benzoate, propylene glycol dibenzoate,2,2,4-trimethyl-1,3-pentanediol dibenzoate,2,2,4-trimethyl-1,3-pentanediol benzoate isobutyrate, 1,3-butanedioldibenzoate, diethylene glycol di-o-toluate, triethylene glycoldi-o-toluate, dipropylene glycol di-o-toluate, 1,2-octyl dibenzoate,tri-2-ethylhexyl trimellitate, di-2-ethylhexyl terephthalate, bis-phenolA bis(2-ethylhexaonate), ethoxylated nonylphenol, and mixtures thereof.Examples of more preferred high refractive index plasticizers aredipropylene glycol dibenzoates and tripropylene glycol dibenzoates.

In addition to the use of a plasticizer, various adhesion control agents(“ACAs”) can be used with the poly(vinyl acetal) resins and in the highM_(w) layers and high Tg layers, and optionally any one or moreadditional layers. ACAs in the multilayer interlayer formulation controladhesion of the interlayer to glass to provide energy absorption onimpact of the glass laminate. In various embodiments of interlayers ofthe present disclosure, the interlayer can comprise about 0.003 to about0.15 parts ACAs per 100 parts resin; about 0.01 to about 0.10 parts ACAsper 100 parts resin; and about 0.01 to about 0.04 parts ACAs per 100parts resin. Such ACAs, include, but are not limited to, the ACAsdisclosed in U.S. Pat. No. 5,728,472 (the entire disclosure of which isincorporated herein by reference), residual sodium acetate, potassiumacetate, magnesium bis(2-ethyl butyrate), and/or magnesiumbis(2-ethylhexanoate).

Anti-blocking agents may also be added to the composition of the presentinvention to reduce the level of blocking of the interlayer.Anti-blocking agents are known in the art, and any anti-blocking agentthat does not adversely affect the properties of the interlayer may beused. A particularly preferred anti-blocking agent that can besuccessfully used as in the multilayer interlayer while not affectingoptical properties of the interlayer or the adhesive properties of theinterlayer to glass is a fatty acid amide (see, for example, U.S. Pat.No. 6,825,255, the entire disclosure of which is incorporated herein).

Other additives may be incorporated into the composition to enhance itsperformance in a final product and impart certain additional propertiesto the interlayer. Such additives include, but are not limited to, dyes,pigments, stabilizers (e.g., ultraviolet stabilizers), antioxidants,flame retardants, IR absorbers or blockers (e.g., indium tin oxide,antimony tin oxide, lanthanum hexaboride (LaB₆) and cesium tungstenoxide), processing aides, flow enhancing additives, lubricants, impactmodifiers, nucleating agents, thermal stabilizers, UV absorbers, UVstabilizers, dispersants, surfactants, chelating agents, couplingagents, adhesives, primers, reinforcement additives, and fillers, amongother additives known to those of ordinary skill in the art.

The high Tg layer, or core layer, or an interlayer sheet that will beused at a high Tg interlayer in the multilayer interlayer structure, hasa melt flow index (“MFI”) of at least 0.65 grams/10 minutes whenmeasured at 190° C. and under a load of 2.16 kilograms. The molecularweight of the poly(vinyl acetal) resin and the amount of plasticizer canbe adjusted to provide an MFI of at least 0.65 grams/10 minutes whenmeasured at 190° C. and under a load of 2.16 kilograms. At these MFIlevels, the high Tg interlayer composition/molten thermoplastic isreasonably flowable and within a commercially acceptable output duringextrusion. The high MFI of the composition with lowered molecular weightresin provides a wider processing window while providing a sheet thathas improved stiffness and Tg. The MFI is desirably at least 0.65, orcan be at least 0.70, or at least 0.80, or at least 0.90, or at least 1,or at least 1.1, or at least 1.2, or at least 1.4, or at least 1.5, orat least 1.8, or at least 2, or at least 3, or at least 5, or at least7, or at least 10, each expressed as grams/10 min. While there is noparticular upper limit, for practical considerations, such as retainingmechanical strength, the MFI should not exceed 40, or should not exceed30, or should not exceed 25 grams/10 min. If the MFI is too low,processability becomes too difficult at commercially useful rates. Ifthe MFI is excessively high, the mechanical properties of the sheet candeteriorate. Suitable ranges include 0.65-40, or 0.65-30, or 0.65-25, or0.7-40, or 0.7-30, or 0.7-25, or 0.8-40, or 0.8-30, or 0.8-25, or0.9-40, or 0.9-30, or 0.9-25, or 1-40, or 1-30, or 1-25, or 1.1-40, or1.1-30, or 1.1-25, or 1.2-40, or 1.2-30, or 1.2-25, or 1.4-40, or1.4-30, or 1.4-25, or 1.5-40, or 1.5-30, or 1.5-25, or 1.8-40, or1.8-30, or 1.8-25, or 2-40, or 2-30, or 2-25, or 3-40, or 3-30, or 3-25,or 5-40, or 5-30, or 5-25, or 7-40, or 7-30, or 7-25, or 10-40, or10-30, or 10-25. The MFI is determined according to ASTM D1238-13,Procedure A.

The thermoplastic composition of the high Tg layers or a one or morecore layers can have a solution viscosity of 120 centipoise (“cps”) orless. The molecular weight of the poly(vinyl acetal) resin and theamount of plasticizer can be adjusted to provide a solution viscosity ofthe high Tg thermoplastic composition (that includes resin andplasticizer) of 125 cps or less. The solution viscosity as used hereinis determined by placing the sheet samples in a crucible overnight todry; determining the sheet sample weight by formula: Wt.sheet=3.195(100+phr)/100; placing the sheet in 4 oz. bottle with 39.57grams Methanol to dissolve; placing the bottle in a constant temperaturewater bath at 20+/−0.1° C. for 1 hour but not to exceed 1.5 hours,placing a viscometer (e.g. Cannon No. 400) in water bath for 5 min. toequilibrate, transferring 10 mls of solution to viscometer by pipette;and timing the solution flow between viscometer marks; then multiplyingthe time (sec.) with the Viscometer factor to determine viscosity in cps(1.038 for the Cannon No. 400). Suitable solution viscosities of thehigh Tg composition or one or more core layers and thermoplasticcomposition include, in cps, are 125 or less, 120 or less, or 110 orless, or 100 or less, or 90 or less, or 85 or less, or 80 or less, or 70or less, or 65 or less, or 60 or less, or 55 or less, or 50 or less, or45 or less, or 40 or less, or 35 or less, or 30 or less. Additionally orin the alternative, the solution viscosity is at least 5 cps, or atleast 10 cps. Suitable ranges of solution viscosity include, in cps,5-125, or 10-125, or 5-120, or 10-120, or 5-110, or 10-110, or 5-100, or10-10, or 5-95, or 10-95, or 5-90, or 10-90, or 5-85, or 10-85, or 5-80,or 10-80, or 5-70, or 10-70, or 5-65, or 10-65, or 5-60, or 10-60, or5-55, or 10-55, or 5-50, or 10-50, or 5-45, or 10-45, or 5-40, or 10-40,or 5-35, or 10-35, or 5-30, or 10-30.

Co-additives such as anti-blocking agents, colorants and UV inhibitors(in liquid, powder, or pellet form) are often used and can be mixed intothe thermoplastic resin or plasticizer prior to arriving in the extruderdevice or combined with the thermoplastic resin inside the extruderdevice. These additives are incorporated into the thermoplasticcomposition, and by extension the resultant multilayer interlayer, toenhance certain properties of the interlayer and its performance in amultiple layer glass panel product (or photovoltaic module).

The multilayer interlayer can be made by any suitable process known toone of ordinary skill in the art of producing interlayers. For example,it is contemplated that the multilayer interlayers may be formed throughdipcoating, solution casting, compression molding, injection molding,melt extrusion, melt blowing or any other procedures for the productionand manufacturing of an interlayer known to those of ordinary skill inthe art.

In some embodiments of the extrusion process, a co-extrusion process maybe utilized. Co-extrusion is a process by which multiple layers ofpolymer material are extruded simultaneously. Generally, this type ofextrusion utilizes two or more extruders to melt and deliver a steadyvolume throughput of different thermoplastic melts of differentviscosities or other properties through a co-extrusion die into thedesired final form. The thickness of the multiple polymer layers leavingthe extrusion die in the co-extrusion process can generally becontrolled by adjustment of the relative speeds of the melt through theextrusion die and by the sizes of the individual extruders processingeach molten thermoplastic resin material.

The high M_(w) layers and high Tg layers can be in direct contact witheach other or can be indirectly disposed adjacent to each other throughanother layer. Desirably, at least one of the high M_(w) layers and atleast one of the high Tg layers are in direct contact with each other.The high M_(w) layers and high Tg layers desirably are also directlybonded to each other. The bond is desirably a heat bond as would occurwhen the layers are laid up against each other and the multilayerinterlayer heated to above the Tg of all layers. This can occur bylaying up the cool layers against each other, or by co-extruding thelayers.

As noted above, the thickness of the multilayer interlayer of theinvention does not have to be increased to obtain a higher E′ modulus.Accordingly the thickness, or gauge, of each interlayer sheet in themultilayer interlayer can be from about at least 5 mils, or at least 10mils, or at least 15 mils, and can be as thick as desired. The sheet canbe as thick as 90 mils, or 120 mils, or more depending on the desiredapplication. Examples of ranges include from about 5 mils to 120 mils(0.12 mm to 3.03 mm), or 15 mils to 90 mils (about 0.38 mm to about2.286 mm), or about 30 mils to about 60 mils (about 0.762 to 1.52 mm),or about 15 mils to about 35 mils (about 0.375 to about 0.89 mm). Thethickness, or gauge, of the multilayer interlayer structure depends onhow many sheets are laminated or co-extruded, and is not particularlylimited, but generally will be greater than 30 mils, or greater than 60mils (1.52 mm) as desired for the particular application.

The multilayer interlayer of the invention also can now be used inapplications which require maintaining good modulus at highertemperatures, such as outdoor applications that undergo regularintermittent stresses, caused by such factors as walking or running, orthat are load bearing under temperature conditions that may exceed 35°C. Examples of applications in which the multilayer interlayer of theinvention is suited include outdoor stairs, outdoor platforms, pavementor sidewalk skylights, ballustrades, curtain walls, flooring, and otherdemanding structural applications.

The multilayer interlayer can be incorporated into a multiple layerpanel. As used herein, a multiple layer panel can comprise a singlesubstrate, such as glass, acrylic, or polycarbonate with a multilayerinterlayer sheet disposed thereon, and most commonly, with a thinpolymer film further disposed over the multilayer interlayer. Thecombination of multilayer interlayer sheet and polymer film is commonlyreferred to in the art as a bilayer. A typical multiple layer panel witha bilayer construct is: (glass) // (multilayer interlayer) //(polymerfilm) where the multilayer interlayer can comprise at least 2interlayers as noted above. The polymer film supplies a smooth, thin,rigid substrate that affords better optical character than that usuallyobtained with a multilayer interlayer alone and functions as aperformance enhancing layer. Polymer films differ from multilayerinterlayers, as used herein, in that polymer films do not themselvesprovide the necessary penetration resistance and glass retentionproperties, but rather provide performance improvements, such asinfrared absorption characteristics. Poly(ethylene terephthalate)(“PET”) is the most commonly used polymer film. Generally, as usedherein, a polymer film is thinner than a multilayer interlayer, such asfrom about 0.001 to 0.2 mm thick.

Further, the multiple layer panel can be what is commonly known in theart as a solar panel, with the panel further comprising a photovoltaiccell, as that term is understood by one of ordinary skill in the art,encapsulated by the multilayer interlayer(s). In such instances, theinterlayer is often laminated over the photovoltaic cell, with aconstruct such as: (glass) // (multilayer interlayer) // (photovoltaiccell) // (multilayer interlayer) // (glass or polymer film).

The interlayers of the present disclosure will most commonly be utilizedin multiple layer panels comprising two substrates, preferably a pair ofglass interlayers, with the interlayers disposed between the twosubstrates. An example of such a construct would be: (glass) //(multilayer interlayer) // (glass), where the multilayer interlayer cancomprise multilayered interlayers as noted above. Further, the multiplelayer panel can contain a polymer film, such as (glass)//(multilayerinterlayer)//polymer film//(glass). These examples of multiple layerpanels are in no way meant to be limiting, as one of ordinary skill inthe art would readily recognize that numerous constructs other thanthose described above could be made with the interlayers of the presentdisclosure.

Such a glass pane structure is further illustrated in FIG. 1. A glasspanel 1 comprises a pair of glass substrates 2, and a multilayerinterlayer 3 containing a first high M_(w) layer 4, a high Tg layer 5,and a second high M_(w) layer 6. The glass panel also contains a bilayerstructure 7 made up of the multilayer interlayer 3 and a polymer film 8.The multilayer interlayer 3 in this case contains a high Tg layerdisposed between two high M_(w) layers. A first side of the high Tglayer 5 is in direct contact with a side of a first high M_(w) layer 4,and a second side of the high Tg layer 5 is also in direct contact witha side of the second high M_(w) layer 6.

The typical glass lamination process comprises the following steps: (1)assembly of the two substrates (e.g., glass) and interlayer; (2) heatingthe assembly via an IR radiant or convective means for a short period;(3) passing the assembly into a pressure nip roll for the firstdeairing; (4) heating the assembly a second time to about 50° C. toabout 120° C. to give the assembly enough temporary adhesion to seal theedge of the interlayer; (5) passing the assembly into a second pressurenip roll to further seal the edge of the interlayer and allow furtherhandling; and (6) autoclaving the assembly at temperatures between 135°C. and 150° C. and pressures between 150 psig and 200 psig for about 30to 90 minutes.

Other means for use in de-airing of the interlayer-glass interfaces(steps 2 to 5) known in the art and that are commercially practicedinclude vacuum bag and vacuum ring processes in which a vacuum isutilized to remove the air.

An alternate lamination process involves the use of a vacuum laminatorthat first de-airs the assembly and subsequently finishes the laminateat a sufficiently high temperature and vacuum.

The high Tg interlayer sheet can be made by any suitable process knownto one of ordinary skill in the art of producing interlayer sheets. Forexample, it is contemplated that the high Tg interlayer sheets may beformed through dipcoating, solution casting, compression molding,injection molding, melt extrusion, melt blowing or any other proceduresfor the production and manufacturing of an interlayer sheet known tothose of ordinary skill in the art.

In one method, the high Tg interlayer sheets can be made by anyconventional sheet extrusion device. The extruder can be a single ortwin screw extruder. There is now also provided a process in which thehigh Tg interlayer poly(vinyl acetal) sheet can be made by:

(i) providing an extrusion system comprising a die and an extruderhaving a barrel;

(ii) feeding a poly(vinyl acetal) resin and a plasticizer into thebarrel and passing a molten thermoplastic composition comprising thepoly(vinyl acetal) resin and plasticizer through the extruder and thedie to produce an extruded sheet, wherein the melt flow index (MFI) ofthe molten thermoplastic resin is at least 0.65 g/10 min when measuredat 190° C. at a loading of 2.16 kilograms; and

(iii) cooling the sheet to produce an interlayer sheet having a glasstransition temperature (Tg) of at least 46.0° C.

Reference to FIG. 2 is made to further illustrate the process of theinvention along with additional features.

As illustrated, there is provided an extrusion system made up of anextruder 1, a filter 2, a die 4, and a melt pump 3 disposed between thefilter 2 and the die 4.

In the extruder device 1, the particles of the thermoplastic composition10 comprising poly(vinyl acetal) resin and plasticizers, and otheradditives described above, are fed through a feed system 11 (e.g.hopper) into the barrel 12 of the extruder 1 and heated by heatingelements 13 to form a molten thermoplastic composition in the barrel 12that is generally uniform in temperature and composition. Generally, inthe extrusion process, thermoplastic resin and plasticizers, includingany of those resins and plasticizers described above, are pre-mixed andfed into an extruder device. For example, the process of the inventioncan include feeding a pre-mix into an extruder 1, wherein the pre-mix isobtained by combining a thermoplastic poly(vinyl acetal) resin and aplasticizer, and optionally other additives first to make a pre-mix, andfeeding the pre-mix to the barrel 12. This method is particularly usefulwhen using a single screw extruder. Alternatively, there can be providedat least two streams fed to the barrel 12 of an extruder (not shown),one stream comprising a poly(vinyl acetal) thermoplastic resin and asecond stream comprising a plasticizer, combining the two streams insidethe barrel of an extruder. This technique is particularly useful whenusing a twin-screw extruder. The at least two streams can be combinedinside the extruder by melting the poly(vinyl acetal) resin inside theextruder in the presence of the plasticizer.

The thermoplastic particles are propelled down the barrel 12 through theaction of the rotating screw 14 powered by a motor 15, and with acombination of shear forces and heat, melts the thermoplastic solidswithin the barrel 12 into a molten thermoplastic composition that ispropelled through a filter 2 to filter out particles. Passage through afilter 2 is a cause for pressure drop, and to compensate, a melt pump 3,such as a gear pump, can be located between the filter 2 and die 4. Theextruder die 4 is the component of the thermoplastic extrusion processwhich gives the final high Tg interlayer sheet product its profile. Aplurality of shapes can be imparted to the end of the high Tg interlayersheet by the die so long as a continuous profile is present.

The thermoplastic composition of the invention is desirably brought to atemperature of 240° C. or less within the barrel 12. When thecomposition experiences temperatures higher than 240° C., there isgenerally a risk of significant build-up of yellow color becausepoly(vinyl acetal) resins tend to form decomposition by-products athigher temperatures. The molten thermoplastic polymer composition isdesirably brought to a temperature within the barrel 12 of 240° C. orless, or 238° C. or less, or 235° C. or less, or 233° C. or less, or232° C. or less, or 230° C. or less, or 228° C. or less, or 226° C. orless, or 225° C. or less, or 220° C. or less, and in each case at atemperature of at least 150° C.

The molten thermoplastic composition is fed from the outlet 16 of themelt pump 3 and fed through a line 17 to a die 4. In this illustration,the thermoplastic composition experiences a pressure drop between theoutlet 16 of the melt pump and the exit to the die 4, and the magnitudeof the pressure drop affects the throughput and capacity of theextrusion process. As the flowability of the thermoplastic compositionincreases so does the throughput of the extrusion device. Theflowability of the thermoplastic composition will manifest itself by thepressure drop between the melt pump and the exit of the die. Since thethermoplastic compositions of the invention are flowable even with lowamounts of plasticizer made possible by the use of poly(vinyl acetal)resins having a low M_(w), it is now possible to process thethermoplastic resin in a commercially acceptable manner while obtainingan interlayer sheet having high Tg. In the process of the invention, areasonable pressure drop across the melt pump outlet and the die exit isobtainable while simultaneously obtaining an interlayer sheet having aTg of 46° C. or more or 50.0° C. or more made at acceptable extrusionrates.

The flowability of the thermoplastic composition in the extruder can beexpressed as a composition having a high melt flow index (MFI) at theconditions in the extruder. The MFI of the thermoplastic composition inthe process of the invention can be at least 0.65 grams/10 min whenmeasured at 190° C. at a loading of 2.16 kilograms.

The interlayer at the state after the extrusion die forms the melt intoa continuous profile will be referred to as an “extruded sheet.” At thisstage in the process, the extrusion die has imparted a particularprofile shape to the thermoplastic composition, thus creating theextruded sheet. The extruded sheet is highly viscous throughout. Atleast a portion or the whole of the extruded sheet as it exits the dieis molten. In the extruded sheet, the thermoplastic composition as itexits the die has not yet been cooled to a temperature at which thesheet generally completely “sets.” Thus, after the extruded sheet leavesthe extrusion die, generally the next step is to cool the polymer meltsheet with a cooling device 5 to make a high Tg interlayer sheet havinga Tg of at least 46.0° C. Cooling devices include, but are not limitedto, spray jets, fans, cooling baths, and cooling rollers. The coolingstep functions to set the extruded sheet into a high Tg interlayer sheetof a generally uniform non-molten cooled temperature. In contrast to theextruded sheet, this interlayer sheet is not in a molten state. Rather,it is the set final form cooled interlayer sheet product. Once theinterlayer sheet has been cooled and set, it is cut with knives 6 andpulled through with a roller/winding system 7.

The high Tg layers or one or more core layers of a multilayer interlayerof the invention desirably has a storage modulus E′ at 40° C. of atleast 300,000,000 pascals, or at least 400,000,000 pascals, or at least500,000,000 pascals, or at least 600,000,000 pascals, or at least700,000,000 pascals, or at least 800,000,000 pascals. There is noparticular upper limit, although practically the monolithic interlayercan obtain an E′ modulus as high as 3,000,000,000 pascals, or as high as2,000,000,000 pascals, or as high as 1,500,000,000 pascals at 40° C.

High Tg layers or one or more core layers of a multilayer interlayer ofthe invention desirably also, or in the alternative, has a storagemodulus E′ at 50° C. of at least 6,000,000 pascals, or at least7,000,000 pascals, or at least 8,000,000 pascals, or at least 9,000,000pascals, or at least 10,000,000 pascals, or at least 20,000,000 pascals,or at least 30,000,000 pascals, or at least 40,000,000 pascals, or atleast 50,000,000 pascals, or at least 60,000,000 pascals, or at least70,000,000 pascals, or at least 80,000,000 pascals, or at least90,000,000 pascals, or at least 100,000,000 pascals. There is noparticular upper limit, although practically the multilayer interlayer(or layers of the multilayer interlayer) can obtain an E′ modulus ashigh as 1,000,000,000 pascals, or as high as 900,000,000 pascals, or ashigh as 800,000,000 pascals at 50° C.

The storage E′ modulus of an interlayer or multilayer interlayer ismeasured according to ASTM D5026-06 (Reapproved 2014). The E′ modulus isobtained by the Dynamic Mechanical Analysis using the RSA-II instrument.A 9 mm wide and 0.765 mm thick sample is clamped at the top and bottomand placed in tension. The length of the sample between the clamps is 22mm. A sinusoidal tensile strain of magnitude 0.01% is applied at afrequency of 1 Hz to the specimen over a range of temperatures and theresulting stress response is measured. Modulus which is a measure ofresistance of the material to deformation is obtained from the ratio ofstress to strain. For an oscillatory tensile deformation, E′ is the realpart of the complex modulus and is referred to as the storage modulus.Temperature control is provided by an oven chamber and the heating rateis 3° C./minute.

Glass panels made with the multilayer interlayers of the invention havethe capability of maintaining acceptable levels of creep resistance,which is 1 mm or less, even at the low poly(vinyl acetal) resinsmolecular weights. Glass panels containing the multilayer interlayers ofthe invention can exhibit a creep of not more than 1 mm at 100° C. andat 1000 hours, or nor more than 0.9 mm, or not more than 0.8 mm, or notmore than 0.7 mm, or not more than 0.6 mm, or not more than 0.5 mm, ornot more than 0.4 mm.

The method for determining creep is to laminate the multilayerinterlayer between two sheet of glass, one sheet measuring 6″×6″ and theother 6″×7″. The glass panel test specimen is hung by the exposed 1″section of glass in an oven set at 100° C. The test specimen is thenremoved at the predetermined intervals and measured to determine howmuch of the 6″×6″ piece of glass has slipped down from its originalposition relative to the 6″×7″ glass. The predetermined intervals are at100, 250, 500, and 1000 hours.

EXAMPLES

A laboratory extrusion trial was conducted using a 1.25″ extruderoutfitted with an extrusion die. The extrusion system is outfitted witha filter at the head of the extruder, followed by a gear pump, followedby the die, and the speed of the gear pump was held constant at 44 rpmfor all examples. The extrusion rate was measured over the course of thetest and was approximately 47-48 g/min for all examples.

Triethylene glycol di-(2-ethylhexanoate) plasticizer (3GEH) was used inall cases, at varying levels as described in the table below. The sameamount of adhesion control agents was added in all cases in the premix.

Pressure transducers were mounted at the outlet of the gear pump. Thepressure at the gear pump relative to the control illustrates the effectof lowering the molecular weight of the PVB resin.

A control Saflex™ DG41 sheet was used to measure Tg and compare with theexperimental cases. Saflex™ DG41 PVB is a commercial product forstructural applications, and was used because it is available in themarketplace.

Table 2 below lists the effect of resin type and plasticizer loading onthe pressure at the outlet of the gear pump, as well as the Tg of theinterlayer for each case. The gear pump pressure is an indicator of animprovement in flowability of the thermoplastic resin in an extrusionenvironment.

TABLE 2 PVB Resin Gear Pump Glass Weight Outlet Transition AveragePlasticizer Pressure Temperature MFI Solution Example MW (phr) (psi) Tg(° C.) (190/2.16) Viscosity 1 (control) 170 20 4466 46.1 0.57 155Saflex ™ DG41 2 (control) 170 20 4240 46.2 Not analyzed Not analyzed 3130 20 3000 45.8 1.40 84.3 4 130 15 3700 51.5 1.03 97.6 5 130 10 439058.8 0.70 82.4 6 50 10 920 60.1 20 14.9

It can be seen that Example 2 demonstrates essentially the same glasstransition temperature as the control sheet of Example 1 (46.2° C. v.46.1° C.). Example 3 demonstrates almost the same glass transitiontemperature (45.8° C.) as Examples 1 and 2, showing that Tg is not afunction of the molecular weight (M_(w)) of the poly(vinyl acetal)resin. Similarly, a comparison of Example 5 and Example 6 alsodemonstrates that the Tg is not a function of the resin molecular weight(M_(w)) since both are plasticized at the same level (10 phr) and havesimilar Tg (58.8° C. v. 60.1° C.).

However, the examples do demonstrate that with a lower molecular weightresin, the amount of plasticizer can be reduced, which in turn elevatesthe Tg of the composition, and that this can be achieved at acceptablerates (as indicated by the lower pressure drop). Examples 4, 5 and 6,which employ a resin having a lower M_(w) and lower amounts ofplasticizer, produce a sheet having a high Tg (exceeding 50° C.). Inaddition, the increase in Tg is not at the expense of acceptable ratesas indicated by pressure drops at about the same amount as the controlor lower.

Example 3, with a lower MW resin and equivalent plasticizer as Examples1 and 2, demonstrates that the molecular weight of the resin allows fora lower pressure at the gear pump due to improved flowability asindicated by its higher MFI value of 1.4 (compared to Example 1 at0.57). Example 6 also demonstrates the same point where the pressurereduction at the gear pump is about 79% relative to Example 1 due to itsdramatically higher MFI of 20 and about 78% relative to Example 2.

Examples 4, 5 and 6 demonstrate that higher Tg monolithic poly(vinylacetal) interlayers can be extruded at lower or almost equivalentpressure drops as Example 2. As the pressure at the gear pump starts toincrease due to further drops in the plasticizer level (as can be seenin Example 5), the flowability of the thermoplastic resin can beimproved by continuing to lower the molecular weight of the resin tocompensate for the low plasticizer levels (as seen in Example 6). Thiseffect can be seen in Example 6 that has the same low plasticizer levelas Example 5, yet has a significantly improved flowability as indicatedby its low pressure requirement and higher MFI, compared to all otherexamples, at the gear pump due to the reduction in molecular weight.

The Examples 3-6 indicate the effect of improved flowability by higherMFI values compared to the control Example 1 employing a resin of higherM_(w). While the MFI starts to decrease as the amount of plasticizer islowered (Examples 3-5), the MFI remains higher than the control and canbe dropped further by employing a resin having a lower M_(w) at the lowplasticizer levels.

Finally, the very low pressure of Example 6 suggests that the resin ofExample 6 can be used in blends with higher molecular weight (M_(w))resins to control process conditions while achieving a higher Tgproduct.

The rheological properties of the interlayer sheets made in Examples 1-6were also studied. FIG. 3 shows that the sheets of Examples 3, 4, 5 and6 possess significantly higher storage modulus E′ at all temperatures of30° C. or more, such as at 40° C. and 50° C. and within the range of30−65° C., or 30-60° C., or 30-55° C., and the differences were quitelarge at 40-55° C., or 40-50° C. The modulus is also higher attemperatures of 50-55° C., suggesting that these formulations performbetter than control Examples 1 and 2 in structural applications that maybe exposed to higher than room temperature conditions.

It is intended that the invention not be limited to the particularembodiments disclosed as the best mode contemplated for carrying outthis invention, and that the invention will include all embodimentsfalling within the scope of the appended claims.

It will further be understood that any of the ranges, values, orcharacteristics given for any single component of the present inventioncan be used interchangeably with any ranges, values, or characteristicsgiven for any of the other components of the invention, wherecompatible, to form an embodiment having defined values for each of thecomponents, as given herein throughout.

1. A multilayer interlayer comprising: (A) a high M_(w) layer comprisinga poly(vinyl acetal) resin having a weight average molecular weight(M_(w)) greater than 160,000 and a plasticizer, wherein the high M_(w)layer has a glass transition temperature (Tg) of less than 46° C.; and(B) a high Tg layer comprising a poly(vinyl acetal) resin having aweight average molecular weight (M_(w)) of 160,000 or less and aplasticizer in an amount of from 2 to 20 parts per hundred parts of thepoly(vinyl acetal) resin, wherein the high Tg layer has a glasstransition temperature (Tg) of at least 46° C.
 2. The multilayerinterlayer of claim 1, wherein the high Tg layer has a solutionviscosity not exceeding 120 cps, and wherein the weight averagemolecular weight (M_(w)) of the poly(vinyl acetal) resin in the high Tglayer does not exceed 100,000.
 3. The multilayer interlayer of claim 1,wherein the high Tg layer comprises poly(vinyl acetal) resin has aweight average molecular weight (M_(w)) not exceeding 150,000 andplasticizer in an amount ranging from about 5 to 20 parts per hundredparts of the poly(vinyl acetal) resin and has a glass transitiontemperature (Tg) of at least 50° C., and the high M_(w) layer comprisespoly(vinyl acetal) resin having a weight average molecular weight(M_(w)) of at least 180,000 and plasticizer in an amount of at least 23phr and has a glass transition temperature (Tg) not exceeding 46° C. 4.The multilayer interlayer of claim 1, wherein the high Tg layer has asolution viscosity not exceeding 120 cps.
 5. The multilayer interlayerof claim 1, the wherein Tg of the high M_(w) layer is at least 4° C.less than the glass transition temperature (Tg) of the high Tg layer. 6.The multilayer interlayer of claim 1, wherein the high Tg layer has amelt flow index (MFI) of at least 0.65 grams/10 minutes when measured at190° C. and under a load of 2.16 kilograms.
 7. A multilayer interlayercomprising: (A) a high M_(w) layer comprising a poly(vinyl acetal) resinhaving a weight average molecular weight (M_(w)) greater than 160,000and a plasticizer, wherein the high M_(w) layer has a glass transitiontemperature (Tg) of less than 46° C.; (B) a high Tg layer comprising apoly(vinyl acetal) resin having a weight average molecular weight(M_(w)) of 150,000 or less and a plasticizer in an amount of from 2 to20 parts per hundred parts of the poly(vinyl acetal) resin, wherein thehigh Tg layer has a glass transition temperature (Tg) of at least 46° C.and a melt flow index (MFI) of at least 0.65 grams/10 minutes whenmeasured at 190° C. and under a load of 2.16 kilograms; and (C) a highM_(w) layer comprising a poly(vinyl acetal) resin having a weightaverage molecular weight (M_(w)) greater than 160,000 and a plasticizer,wherein the high M_(w) layer has a glass transition temperature (Tg) ofless than 46° C., wherein the high Tg layer is disposed between the highM_(w) layers.
 8. The multilayer interlayer of claim 7, wherein the highTg layer has a solution viscosity not exceeding 120 cps.
 9. Themultilayer interlayer of claim 7, the wherein glass transitiontemperature (Tg) of at least one of the high M_(w) layers is at least 4°C. less than the glass transition temperature (Tg) of the high Tg layer.10. The multilayer interlayer of claim 7, wherein the high Tg layercomprises poly(vinyl acetal) resin having a weight average molecularweight (M_(w)) not exceeding 150,000 and plasticizer in an amountranging from about 5 to 20 parts per hundred parts of the poly(vinylacetal) resin and has a glass transition temperature (Tg) of at least50° C., and wherein at least one of the high M_(w) layers comprisespoly(vinyl acetal) resin having a weight average molecular weight(M_(w)) of at least 180,000 and plasticizer in an amount of at least 23phr and has a glass transition temperature (Tg) not exceeding 46° C. 11.The multilayer interlayer of claim 7, wherein the high Tg layercomprises poly(vinyl acetal) resin having a weight average molecularweight (M_(w)) that does not exceed 140,000 in the high Tg layer andplasticizer in an amount ranging from 2 to 20 parts per hundred parts ofthe poly(vinyl acetal) resin.
 12. The multilayer interlayer of claim 7,wherein the high Tg layer has a melt flow index (MFI) of at least 0.70grams/10 minutes when measured at 190° C. and under a load of 2.16kilograms.
 13. A multilayer interlayer comprising: (A) a high M_(w)layer comprising a poly(vinyl acetal) resin having a weight averagemolecular weight (M_(w)) greater than 160,000 and a plasticizer, whereinthe high M_(w) layer has a glass transition temperature (Tg) of lessthan 46° C.; (B) a high Tg layer comprising a poly(vinyl acetal) resinhaving a weight average molecular weight (M_(w)) of 150,000 or less anda solution viscosity not exceeding 120 cps, and a plasticizer in anamount of from 2 to 20 parts per hundred parts of the poly(vinyl acetal)resin, wherein the high Tg layer has a glass transition temperature (Tg)of at least 46° C.; and (C) a high M_(w) layer comprising a poly(vinylacetal) resin having a weight average molecular weight (M_(w)) greaterthan 160,000 and a plasticizer, wherein the high M_(w) layer has a glasstransition temperature (Tg) of less than 46° C., wherein the high Tglayer is disposed between the high M_(w) layers.
 14. The multilayerinterlayer of claim 13, the wherein glass transition temperature (Tg) ofat least one of the high M_(w) layers is at least 4° C. less than theglass transition temperature (Tg) of the high Tg layer.
 15. Themultilayer interlayer of claim 13, wherein the high Tg layer plasticizerin an amount ranging from about 5 to 20 parts per hundred parts of thepoly(vinyl acetal) resin and has a glass transition temperature (Tg) ofat least 50° C., and wherein at least one of the high M_(w) layerscomprises poly(vinyl acetal) resin having a weight average molecularweight (M_(w)) of at least 180,000 and plasticizer in an amount of atleast 23 phr and has a glass transition temperature (Tg) not exceeding46° C.
 16. The multilayer interlayer of claim 13, wherein the high Tglayer comprises poly(vinyl acetal) resin having a weight averagemolecular weight (M_(w)) that does not exceed 140,000 in the high Tglayer and plasticizer in an amount ranging from 2 to 20 parts perhundred parts of the poly(vinyl acetal) resin.
 17. The multilayerinterlayer of claim 13, wherein the high Tg layer has a melt flow index(MFI) of at least 0.65 gram/10 minutes when measured at 190° C. andunder a load of 2.16 kilograms.
 18. The multilayer interlayer of claim17, wherein the high Tg layer has a melt flow index (MFI) of at least0.70 grams/10 minutes when measured at 190° C. and under a load of 2.16kilograms.